The present invention relates to a fuel injector for an internal-combustion engine.
For operation of fuel injection systems in which fuel is stored under high pressure in a preliminary storage tank and, in response to a control signal supplied from the outside, is injected by fuel injectors during a defined injection interval into the combustion space of an internal-combustion engine (common-rail systems), fuel injectors have become known for selective or simultaneous actuation using various fuels; such fuels may, for example, be a liquid fuel, such as Diesel oil, and a gaseous fuel, such as a combustible gas.
A fuel injector of this type contains a first injection valve, which is arranged in a valve housing and contains a first valve member which can be axially displaced between a closed position and an open position, for injecting a first fuel into the combustion space of the internal-combustion engine, as well as a first actuating device, which is coupled directly or by way of a first actuating element with the first valve member and is provided in the valve housing axially behind the first injection valve, for opening and closing the first injection valve. Furthermore, the fuel injector contains at least one second injection valve, which is arranged in the valve housing and contains a second valve member which can be axially displaced between a closed position and an open position, for injection of at least one second fuel into the combustion space of the internal-combustion engine, as well as at least one second actuating device, which is coupled with the second valve member, for opening and closing the second injection valve.
A fuel injector of this type is known, for example, from European Patent Document EP 0 575 887 A1. In this known fuel injector, the valve member of the first injection valve is controlled directly by being acted upon by a hydraulic closing pressure. The valve member of the second injection valve is controlled by way of a double-piston arrangement which is also acted upon by the hydraulic closing pressure.
One difficulty in the construction of fuel injectors for several fuels is that, on the one hand, the arrangement of several actuating devices for the various fuels in the fuel injector requires a relatively large amount of space, and, on the other hand, the space which is available for the fuel injectors on an internal-combustion engine, such as a Diesel engine, is limited.
It is therefore an object of the invention to provide a fuel injector, for an internal-combustion engine which has several injection valves for operation with several fuels, in which the actuating devices for the various injection valves are arranged in a space-saving manner.
The fuel injector according to the invention contains a first injection valve, which is arranged in a valve housing and contains a first valve member which can be axially displaced between a closed position and an open position, for injecting a first fuel into the combustion space of the internal-combustion engine, as well as a first actuating device, which is coupled directly or by way of a first actuating element with the first valve member and is provided in the valve housing axially behind the first injection valve, for opening and closing the first injection valve. At least one second injection valve is arranged in the valve housing and contains a second valve member which can be axially displaced between a closed position and an open position. The at least one second injection value is used for injecting at least one second fuel into the combustion space of the internal-combustion engine. At least one second actuating device is coupled with the second valve member for opening and closing the second injection valve. According to the invention, the valve member of the second injection valve is arranged radially at a distance from the valve member of the first injection valve in the valve housing, the second actuating device is arranged axially downstream of the first actuating device in the valve housing, and the valve member of the second injection valve is coupled with the second actuating device by way of a second actuating element which is axially displaceably disposed in the valve housing and surrounds the first actuating device.
The significant advantage of the fuel injector according to the invention is that its valve housing can be manufactured with a very small diameter. This permits the use of the fuel injector when the space available on the internal-combustion engine is very limited and allows operation by way of several fuels. Another advantage is the possibility of a centric arrangement of the injection valve, which simplifies the manufacturing of the fuel injector.
Advantageously, at least two second injection valves which have valve members radially spaced from the valve member of the first injection valve are arranged in the valve housing.
In such an embodiment, it is advantageous to arrange the valve members of the second injection valves essentially diametrically with respect to the valve member of the first injection valve.
According to a particularly advantageous embodiment of the fuel injector according to the invention, the second actuating element contains several tappet-type actuating members which are disposed in an axially displaceable manner radially outside the first actuating device in the valve housing. This permits a slim construction and therefore a low space requirement.
Advantageously, the second actuating element contains a yoke, arranged at the end side, for coupling the tappet-type actuating members with the second actuating device.
This construction may advantageously be further developed by providing the yoke with a plate shape and, for joint actuation of the tappet-type actuating members, by centrically coupling the yoke with the second actuating device.
The yoke advantageously has radially extending arms for actuating the tappet-type actuating members. The number of arms corresponds to the number of the tappet-type actuating members, each of which is arranged coaxially with respect to the others.
The number of the tappet-type actuating members advantageously corresponds to the number of the second injection valves.
In this case, it is particularly advantageous for each of the tappet-type actuating members to be arranged coaxially with respect to the valve members of the second injection valves.
Advantageously, the tappet-type actuating members are arranged on the same radius with respect to the injector axis.
According to a further development of the fuel injector according to the invention, the second actuating element contains a ring element arranged, at the end side, for the coupling of the valve members of the second injection valves with the tappet-type actuating members. In this case, the ring element surrounds the first actuating device or the valve member and/or the first actuating element of the first injection valve.
The above-mentioned embodiment may be further developed by providing the ring element with radially inwardly projecting arms for actuating the valve members of the second injection valves.
According to another advantageous embodiment of the fuel injector according to the invention, the valve housing is constructed in several parts, and the second actuating element, together with the first actuating device, is housed in a separate housing part in which the tappet-type actuating members are axially displaceably disposed. This represents a significant simplification with respect to the production, the assembly and the maintenance of the fuel injector.
According to a further advantageous embodiment of the fuel injector according to the invention, the tappet-type actuating members, together with the yoke arranged on the end side and/or the ring element arranged on the end side, form an actuating arrangement which surrounds the first actuating device in a cage-type manner.
In this case, the cage arrangement formed by the tappet-type actuating members and the yoke arranged on the end side and/or the ring element arranged on the end side are advantageously accommodated in the second housing part. The yoke arranged on the end side is disposed at one side and/or the ring element arranged on the end side is arranged at the other end of the separate housing part.
In the valve housing, the fuel injector advantageously has one or several fuel ducts which extend, at least in sections, inside this actuating cage.
In this case, the fuel ducts can be spaced radially and/or in the circumferential direction away from the tappet-type actuating members of the actuating cage.
According to an alternative embodiment of the fuel injector according to the invention, an actuating device, coupled with the valve member of the second injection valve, is provided for each individual second injection valve or in each case for several of the second injection valves. This permits actuating each individual second injection valve or groups of several of the second injection valves independently of one another.
This embodiment may be further developed by coupling the actuating devices in each case by way of a tappet-type actuating element with the valve member of the assigned second injection valve.
In the fuel injector according to the invention, the first actuating device may be constructed as an electromagnetic actuating device.
The second actuating device of the fuel injector according to the invention may be constructed as a mechanical or hydromechanical actuating device.
According to an advantageous embodiment, the fuel injector according to the invention is constructed for optional operation with diesel oil and/or a gaseous fuel. The first injection valve is provided for feeding diesel oil and the second injection valves are provided for feeding the gaseous fuel.
An embodiment of the fuel injector according to the invention will be explained in the following by way of reference to the drawing figures.